Seafloor evidence for pre-shield volcanism above the Tristan da Cunha mantle plume

Abstract

Tristan da Cunha is assumed to be the youngest subaerial expression of the Walvis Ridge hot spot. Based on new hydroacoustic data, we propose that the most recent hot spot volcanic activity occurs west of the island. We surveyed relatively young intraplate volcanic fields and scattered, probably monogenetic, submarine volcanoes with multibeam echosounders and sub-bottom profilers. Structural and zonal GIS analysis of bathymetric and backscatter results, based on habitat mapping algorithms to discriminate seafloor features, revealed numerous previously-unknown volcanic structures. South of Tristan da Cunha, we discovered two large seamounts. One of them, Isolde Seamount, is most likely the source of a 2004 submarine eruption known from a pumice stranding event and seismological analysis. An oceanic core complex, identified at the intersection of the Tristan da Cunha Transform and Fracture Zone System with the Mid-Atlantic Ridge, might indicate reduced magma supply and, therefore, weak plume-ridge interaction at present times.

Plume–ridge interactions: ridgeward versus plate-drag plume flow

“…1a; Ito et al, 2003). Plume-ridge interaction is manifested by geophysical and geochemical anomalies along the ridge axis, e.g., high mantle potential temperature (Dalton et al, 2014), enriched radiogenic isotope anomalies (Cushman et al, 2004;Douglass et al, 1999;Yang et al, 2017) and adjacent lineations of seamounts (Ballmer et al, 2013b;Geissler et al, 2020;Lénat et al, 2009). Furthermore, plumes may promote migration of MOR spreading centers (Müller et al, 1998;Mittelstaedt et al, 2008Mittelstaedt et al, , 2011Whittaker et al, 2015), as evidenced by successive ridge jumps towards mantle plumes, e.g., at Iceland, Amsterdam-Saint Paul and Galapagos hotspots (Hardarson et al, 1997;Maia et al, 2011;Mittelstaedt et al, 2012).…”

Cetaceans Sightings During Research Cruises in Three Remote Atlantic British Overseas Territories

“…Despite their different climate zones, all three territories are characterized by deep oceans with steep-sided volcanic seamounts and guyots rising from the deep ocean floor (Makler and de Matos Mello, 2007;Geissler et al, 2020); only the island of South Georgia has a significant area of shelf shallower than 700m deep distinguishing it from the rest of SGSSI (Hogg et al, 2016) and the Atlantic territories. The seamounts and shelf breaks provide upwelling areas of productivity, supporting a rich food chain that includes many cetacean species (MacLeod and Bennett, 2007;Rossi-Santos et al, 2007;Best et al, 2009;Calderan et al, 2020;Jackson et al, 2020).…”